Let's think about the clues in the riddle:
- It is small.
- It has a spiky back.
- It curls up into a ball to protect itself and not become a snack.
What animal fits this description? It's a hedgehog! Hedgehogs are little animals covered with sharp spines on their backs. When they feel scared or threatened, they curl up into a tight ball, so their spiky back faces outwards, protecting them from predators. This clever defense makes it hard for other animals to eat them.
So, the answer to the riddle is: hedgehog.